1. Field of the Invention
The present invention relates to a tomographic X-ray apparatus for dental and otolaryngological diagnosis for photographing the head or maxillofacial region of a patient.
2. Description of the Prior Art
Dental rotational tomographic X-ray apparatuses, generally referred to as dental panoramic X-ray apparatuses in the field of dental diagnosis, are known and used widely even at small dental clinics. The general types of these apparatuses comprise an X-ray source and an X-ray film disposed at opposite ends of a rotary arm, with the head of a patient positioned therebetween. The rotary arm is not necessarily to be formed in the shape of a slender rod. A ring-shaped rotary arm is also known as described in U.S. Pat. No. 4,847,881 for example.
These days, in addition to the above-mentioned rotational tomographic X-ray apparatuses, there have been demands for planigraphic X-ray apparatuses for selectively photographing specific regions in narrow tomographic widths. Such planigraphic X-ray apparatuses conventionally used for general medical diagnosis are large in size and thus require a wide installation space. In addition, they are expensive despite of having a single-purpose function only. Accordingly, the conventional apparatuses have not been used widely at general dental clinics other than relatively large-sized hospitals.
As the above-mentioned conventional planigraphic X-ray apparatuses, various types are known, such as a tomography type wherein the X-ray source and the film supported by a rotary arm perform symmetric rotational motions around the rotation center of the rotary arm, a planigraphy type wherein the X-ray source and the film perform linear motions in parallel and a multiple track type wherein the X-ray source and the film perform motions along curved tracks. These types, however, have relatively wide photographing areas so that they can be used to mainly photograph abdominal regions. In addition, the rotary arm of each of these types is rotated around a fixed point. For these reasons, it is difficult to change the magnifying ratio of the X-ray image to be obtained. Furthermore, it is necessary to preserve a rotation range for the rotary arm, causing the problem of requiring a wide installation space.
Accordingly, these days, X-ray apparatuses having various photographing functions have been proposed for the purpose of diagnosis in dental, otolaryngological and oral surgery fields.
Japanese Laid-open Patent Application No. 58-165825, for example, discloses an apparatus which is capable of performing both planiographic photographing and rotational tomographic photographing. This apparatus, however, has no means for controlling the rotation angle of the X-ray generator thereof. In addition, when the apparatus performs planiographic photographing, the film transfer mechanism thereof is stopped and the rotary arm is rotated, and then the entire region of an X-ray image is exposed once while the film is held stationary. With this method, distortion is apt to be caused in photographed X-ray images, and the magnifying ratio of the X-ray image to be obtained in the case of planigraphic photographing cannot be changed.
The apparatus disclosed by the above-mentioned U.S. Pat. No. 4,847,881 can perform rotational tomographic photographing of dental arches and obtain slice tomogram images of temporomandibular joints. The slice tomogram method used for this apparatus, however, is not classified as planigraphic photographing but classified as rotational tomographic photographing having a narrow tomographic width. Besides, since the apparatus has no mechanism for planigraphic photographing, it cannot perform planigraphic photographing.